/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.table.runtime.operators.window.triggers;

import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.common.state.ReducingState;
import org.apache.flink.api.common.state.ReducingStateDescriptor;
import org.apache.flink.api.common.typeutils.base.LongSerializer;
import org.apache.flink.table.runtime.operators.window.Window;

import java.time.Duration;

import static org.apache.flink.util.Preconditions.checkArgument;
import static org.apache.flink.util.Preconditions.checkNotNull;

/**
 * A {@link Trigger} that reacts to processing-time timers.
 * The behavior can be one of the following:
 * <p><ul>
 *     <li> fire when the processing time passes the end of the
 *          window ({@link ProcessingTimeTriggers#afterEndOfWindow()}),
 *     <li> fire when the processing time advances by a certain interval
 *          after reception of the first element after the last firing for
 *          a given window ({@link ProcessingTimeTriggers#every(Duration)}).
 * </ul></p>
 * In the first case, the trigger can also specify an <tt>early</tt> trigger.
 * The <tt>early trigger</tt> will be responsible for specifying when the trigger should fire in the period
 * between the beginning of the window and the time when the processing time passes the end of the window.
 */
public class ProcessingTimeTriggers {

	private static final String TO_STRING = "ProcessingTime.afterEndOfWindow()";

	/**
	 * This class should never be instantiated.
	 */
	private ProcessingTimeTriggers() {}

	/**
	 * Creates a trigger that fires when the processing time passes the end of the window.
	 */
	public static <W extends Window> AfterEndOfWindow<W> afterEndOfWindow() {
		return new AfterEndOfWindow<>();
	}

	/**
	 * Creates a trigger that fires by a certain interval after reception of the first element.
	 * @param time the certain interval
	 */
	public static <W extends Window> AfterFirstElementPeriodic<W> every(Duration time) {
		return new AfterFirstElementPeriodic<>(time.toMillis());
	}

	/**
	 * Trigger every a given interval, the first trigger time is interval
	 * after the first element in the pane.
	 *
	 * @param <W> type of window
	 */
	public static final class AfterFirstElementPeriodic<W extends Window> extends Trigger<W> {

		private static final long serialVersionUID = -4710472821577125673L;

		private final long interval;
		private final ReducingStateDescriptor<Long> nextFiringStateDesc;

		private transient TriggerContext ctx;

		AfterFirstElementPeriodic(long interval) {
			checkArgument(interval > 0);
			this.interval = interval;
			this.nextFiringStateDesc = new ReducingStateDescriptor<>(
					"processingTime-every-" + interval, new Min(), LongSerializer.INSTANCE);
		}

		@Override
		public void open(TriggerContext ctx) throws Exception {
			this.ctx = ctx;
		}

		@Override
		public boolean onElement(Object element, long timestamp, W window) throws Exception {
			ReducingState<Long> nextFiring = ctx.getPartitionedState(nextFiringStateDesc);
			if (nextFiring.get() == null) {
				long nextTimer = ctx.getCurrentProcessingTime() + interval;
				ctx.registerProcessingTimeTimer(nextTimer);
				nextFiring.add(nextTimer);
			}
			return false;
		}

		@Override
		public boolean onProcessingTime(long time, W window) throws Exception {
			ReducingState<Long> nextFiring = ctx.getPartitionedState(nextFiringStateDesc);
			Long timer = nextFiring.get();
			if (timer != null && timer == time) {
				long newTimer = time + interval;
				ctx.registerProcessingTimeTimer(newTimer);
				nextFiring.clear();
				nextFiring.add(newTimer);
				return true;
			} else {
				return false;
			}
		}

		@Override
		public boolean onEventTime(long time, W window) throws Exception {
			return false;
		}

		@Override
		public boolean canMerge() {
			return true;
		}

		@Override
		public void onMerge(W window, OnMergeContext mergeContext) throws Exception {
			mergeContext.mergePartitionedState(nextFiringStateDesc);

			// after merge, the merged state will be stored in current window
			Long nextTimer = ctx.getPartitionedState(nextFiringStateDesc).get();
			if (nextTimer != null) {
				ctx.registerProcessingTimeTimer(nextTimer);
			}
		}

		@Override
		public void clear(W window) throws Exception {
			ReducingState<Long> nextFiring = ctx.getPartitionedState(nextFiringStateDesc);
			Long timer = nextFiring.get();
			if (timer != null) {
				ctx.deleteProcessingTimeTimer(timer);
				nextFiring.clear();
			}
		}

		@Override
		public String toString() {
			return "ProcessingTime.every(" + interval + ")";
		}

		private static class Min implements ReduceFunction<Long> {
			private static final long serialVersionUID = 1L;

			@Override
			public Long reduce(Long value1, Long value2) throws Exception {
				return Math.min(value1, value2);
			}

		}
	}

	/**
	 * A {@link Trigger} that fires once the current system time passes the end of the window
	 * to which a pane belongs.
	 */
	public static final class AfterEndOfWindow<W extends Window> extends Trigger<W> {
		private static final long serialVersionUID = 2369815941792574642L;

		/**
		 * Creates a new {@code Trigger} like the this, except that it fires repeatedly whenever
		 * the given {@code Trigger} fires before the processing time has passed the end of the window.
		 */
		public AfterEndOfWindowNoLate<W> withEarlyFirings(Trigger<W> earlyFirings) {
			checkNotNull(earlyFirings);
			return new AfterEndOfWindowNoLate<>(earlyFirings);
		}

		private TriggerContext ctx;

		@Override
		public void open(TriggerContext ctx) throws Exception {
			this.ctx = ctx;
		}

		@Override
		public boolean onElement(Object element, long timestamp, W window) throws Exception {
			ctx.registerProcessingTimeTimer(window.maxTimestamp());
			return false;
		}

		@Override
		public boolean onProcessingTime(long time, W window) throws Exception {
			return time == window.maxTimestamp();
		}

		@Override
		public boolean onEventTime(long time, W window) throws Exception {
			return false;
		}

		@Override
		public void clear(W window) throws Exception {
			ctx.deleteProcessingTimeTimer(window.maxTimestamp());
		}

		@Override
		public boolean canMerge() {
			return true;
		}

		@Override
		public void onMerge(W window, OnMergeContext mergeContext) throws Exception {
			ctx.registerProcessingTimeTimer(window.maxTimestamp());
		}

		@Override
		public String toString() {
			return TO_STRING;
		}
	}

	/**
	 * A composite {@link Trigger} that consist of AfterEndOfWindow and a early trigger.
	 */
	public static final class AfterEndOfWindowNoLate<W extends Window> extends Trigger<W> {

		private static final long serialVersionUID = 2310050856564792734L;

		// early trigger is always not null
		private final Trigger<W> earlyTrigger;
		private TriggerContext ctx;

		AfterEndOfWindowNoLate(Trigger<W> earlyTrigger) {
			checkNotNull(earlyTrigger);
			this.earlyTrigger = earlyTrigger;
		}

		@Override
		public void open(TriggerContext ctx) throws Exception {
			this.ctx = ctx;
			earlyTrigger.open(ctx);
		}

		@Override
		public boolean onElement(Object element, long timestamp, W window) throws Exception {
			ctx.registerProcessingTimeTimer(window.maxTimestamp());
			return earlyTrigger.onElement(element, timestamp, window);
		}

		@Override
		public boolean onProcessingTime(long time, W window) throws Exception {
			return time == window.maxTimestamp() || earlyTrigger.onProcessingTime(time, window);
		}

		@Override
		public boolean onEventTime(long time, W window) throws Exception {
			return earlyTrigger.onEventTime(time, window);
		}

		@Override
		public boolean canMerge() {
			return earlyTrigger.canMerge();
		}

		@Override
		public void onMerge(W window, OnMergeContext mergeContext) throws Exception {
			ctx.registerProcessingTimeTimer(window.maxTimestamp());
			earlyTrigger.onMerge(window, mergeContext);
		}

		@Override
		public void clear(W window) throws Exception {
			ctx.deleteProcessingTimeTimer(window.maxTimestamp());
			earlyTrigger.clear(window);
		}

		@Override
		public String toString() {
			StringBuilder builder = new StringBuilder(TO_STRING);
			if (earlyTrigger != null) {
				builder
					.append(".withEarlyFirings(")
					.append(earlyTrigger)
					.append(")");
			}
			return builder.toString();
		}
	}
}
